This application is based on patent application No. 10-359726 filed in Japan, the contents of which are hereby incorporated by references.
The present invention relates to a golf ball having a coating layer which is excellent in resistance to impact and scuffing. More particularly, a golf ball having a coating layer which has a high hardness with a small thickness.
A golf ball generally has a coating layer enclosing a main body of the golf ball in order to provide gloss to the golf ball surface. However, it is difficult to maintain the gloss for a long time, since the golf ball is used in various severe circumstances. Therefore, the coating layer of the golf ball is required to satisfy the following properties: 1) flexibility capable of preventing cracking even due to extremely large deformation of the ball resulting from, for example, an impact of a driver shot; 2) high scuffing resistance capable of preventing damages due to large friction resulting from an iron shot; 3) high abrasion resistance capable of preventing abrasion due to a bunker shot; 4) high impact resistance capable of preventing peeling of the coating layer from the golf ball main body due to hit by golf clubs; and 5) high waterproof capable of preventing peeling of the coating layer due to use in the rain.
To improve impact and scuffing resistance of a golf ball, Japanese Unexamined Patent Publication No. 9-59566 discloses a coating material for a golf ball obtained by mixing a specified polyurethane polyol with non-yellowing polyisocyanate. However, since the coating material forms a soft coating layer for the purpose of increasing its impact resistance, the formed layer is poor in scuffing and abrasion resistance.
In addition, material for a driver club has recently changed from woods into hard metals such as titanium (Vickers hardness 300), and material for an iron club has also changed from mild steel (Vickers hardness 200) into stainless steel (Vickers hardness 360). These new clubs are likely to cause more severe cracks and abrasion in the golf ball surface than conventional clubs. Thus, a demand has been increasing for a golf ball having increased scuffing and abrasion resistance.
One of the solutions for improving scuffing and abrasion resistance may be to increase the thickness of a coating layer of a golf ball. This solution, however, is likely to deform a dimple structure formed on the golf ball surface and thereby make different flight curve from that of the conventional golf ball. Thus, the golf ball having a thick coating layer may not be for practical use. Also, a thicker coating layer needs higher cost of a coating material for the layer.
An object of the present invention is to provide a golf ball having a coating layer which is excellent in scuffing and abrasion resistance without increasing the layer thickness.
According to an aspect of the present invention, a golf ball having a main body and a coating layer enclosing the main body. The coating layer has a thickness of 5 to 20 xcexcm and a hardness of 21 to 60 N/mm2. The hardness is calculated according to the following expression (1),
Hardness=(test load)/{26.43xc3x97(penetration depth (mm))2}xe2x80x83xe2x80x83(1)
wherein the test load is 3 mN.